In a conventional vehicle, the various electronic components and systems are either directly connected to the vehicle's power supply, resulting in a constant drain on the power supply, or activated via a power relay that is controlled by the vehicle's ignition switch. For a two-position ignition switch, the systems coupled to the vehicle's power supply via the ignition switch are all either off or on, and when they are turned on they are activated simultaneously. Many vehicles, however, use a four-position or a five-position ignition switch, thereby allowing the user to activate some of the vehicle's accessory systems without applying power to all of the vehicle's electronic components and systems. In a four-position switch the positions typically correspond to (i) off, (ii) accessories, (iii) on, and (iv) start, while in a five-position switch the positions typically correspond to (i) off, (ii) accessories 1, (iii) accessories 2, (iv) on, and (v) start. Note that the “start” position only relates to vehicles that utilize an internal combustion engine (ICE), and therefore require the use of a starter motor to initiate engine operation. Accessories that may be powered-on when the ignition switch is in an accessory position include internal lights, external lights, power windows, ventilation blower fans, and the vehicle's entertainment system. Always on components and systems, i.e., those systems that are directly connected to the vehicle's power supply and therefore are always in a powered-up state, typically include power door locks, alarm systems, subsystem monitors, and some or all vehicle lights.
While the conventional power system is adequate, it can lead to undesired consequences. For example, when a conventional vehicle is left unattended for an extended period of time such as when the user is away on vacation, the power drain from the directly connected systems can completely drain the battery, thereby leaving the user stranded when they return to their car. Additionally, since those systems that are powered-up by the ignition switch are all turned on at one time, electronic controller diagnostic strategies are often unnecessarily complex. Accordingly, what is needed is a power distribution system that provides more control over the various electronic components and systems of a vehicle during the power-up sequence. The present invention provides such a system.